ASoC: Return proper error for omap3pandora_soc_init

Return PTR_ERR(omap3pandora_dac_reg) instead of 0 if regulator_get failed.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>